Studies on the size,location and turnover of calcium pools accessible to growing Tetrahymena cells

Tetrahymena pyriformis cells in the logarithmic phase of growth accumulate 2.5–3.75 times as much calcium per unit volume as is present in the growth medium. It appears that most of this calcium is stored in a non-ionic form, with approximately 30% existing in the cilia, near its site of action in effecting ciliary reversal. The exchange of extracellular ⁴⁵Ca²⁺ with the major internal pools is extremely rapid, exhibiting a $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of less than 0.5 h. Sites located on the cilia are responsible for 35–50% of Ca²⁺ influx, with the remainder entering through other positions on the cell surface.     

Thyroid hormones and muscle protein turnover. The effect of thyroid-hormone deficiency and replacement in thryoidectomized and hypophysectomized rats.

We have investigated the effects of thyroidectomy, hypophysectomy and 3,3',5-tri-iodothyronine replacement on protein synthesis and degradation in skeletal muscle in vivo. Thyroidectomy resulted in a decrease in the rate of protein synthesis as a result of a loss of RNA. However, RNA activity, the rate of protein synthesis per unit of RNA, was not decreased. This was the case in both young growing rats and mature nongrowing rats. Tri-iodothyronine treatment of thyroidectomized rats increased protein synthesis by increasing RNA concentration without changes in RNA activity, and this occurred even when food intake was restricted to prevent any increase in growth. The rate of protein degradation was decreased by thyroidectomy and increased by tri-iodo-thyronine replacement in both animals fed ad libitum and food-restricted animals. Hypophysectomy decreased protein synthesis by decreasing both RNA concentration and activity. these changes were reversed by tri-iodothyronine treatment even in the presence of persistent marked hypoinsulinaemia. This indicates that tri-iodothyronine can activate athe translational phase of protein synthesis in muscle in the absence of significant quantities of insulin. However, tri-iodothyronine does not seem to be obligatory for the maintenance of normal RNA activity in muscle, since in the thyroidectomized rat, in which plasma insulin concentrations are normal, RNA activity is maintained. From a consideration of the magnitude of changes in RNA activity observed in these experiments, it would appear that alterations in rates of elongation as well as initiation are involved in the changes in RNA activity.     

The structure of immunoglobulin variable regions in the horned shark,Heterodontus francisci

The heavy and light chains of pooled antibodies of the hybodont shark,Heterodontus francisci (horned shark), were subjected to amino acid sequence analysis. Yield determinations showed that more than 90% of the available polypeptides in the respective pools were sequenced. The heavy chains were homogeneous in the initial framework segment and showed a sequence homology of approximately 70% with the corresponding region of the more recently evolved nurse shark and a 45% homology with a human myeloma heavy chain. The light chains were less homogeneous and not identifiable as either kappa or lambda chains as known in higher species. The first half-cystine characteristics of the variable domain intrachain disulfide bridge of immunoglobulins was present in the same position (22 for heavy chains; 23 for light chains) in the horned shark as in mammalian species. The sequence analysis also suggested the presence of a hypervariable region in the horned shark light chains. The combined data imply that the antigen-binding function of immunoglobulins is mediated in much the same manner in this primitive shark as in more recently evolved species, including mammals.     

Functional analysis of frog pectoral girdles. The epicoracoid cartilages

Two types of pectoral girdles occur among frogs. Arciferal girdles have overlapping epicoracoid cartilages; in firmisternal girdles the epicoracoid cartilages are fused along the ventral midline. Cineradiographic experiments of jumping frogs show that the epicoracoid cartilages of arciferal girdles move relative to each other at the time of landing. Recordings of landings on a force platform reveal that the pectoral girdle of frogs is loaded compressively through the glenoid. This loading regime coupled with differential mobility between firmisternal and arciferal girdles results in differences in stress distribution in the two girdles during landing. The patterns of stress distribution suggest that variation seen among frogs in other aspects of pectoral morphology in addition to the condition of the epicoracoid cartilages may be best understood when analysed from a biomechanical perspective.     

The flight mechanism of the pigeon Columbia livia during take-off

High-speed film analysis of the mechanism of take-off of a pigeon ascending nearly vertically reveals the pattern of movements of the wing segments and the bones within them during each of the five phases of the wingbeat cycle. Differences in the type and extent of wing movements between the upstroke and downstroke portions of the first and successive wingbeat cycles are explained with reference to the upward vertical jump made during the first wingbeat cycle. The presence during pigeon take-off of a non-steady state pattern of airfoil action similar to that seen in some insects at the beginning of the downstroke was verified.     

Increased in vitro labeling of stable RNA within the rat nodose ganglion following abdominal vagotomy

An in vitro procedure for labeling of RNA in the excised rat nodose ganglion was used to evaluate the changes in incorporation of [³H]uridine into ganglionic RNA following transection of the abdominal vagus nerves. Significant increases in the incorporation into 28S, 18S and 4S RNA were observed at 1 day after injury, which were maximal at 4 days before returning to unoperated control level by 7 days. A second transient increase in the labelling of these RNA species occurred between 9 and 11 days after injury. Comparison of the time course of these increases with those seen previously following cervical vagus nerve crush injury indicate that the time of onset of the increase in incorporation is independent of the site of injury, but that the maximal response is delayed by 1 day with the more distal lesion. These data are consistent with the existence of separate signals for initiating and modulating the cell body response to axon injury, which are transported retrogradely from the site of injury at rates exceeding the slow component of axoplasmic transport.     

Embryogenesis in the Presence of Blockers of Mechanosensitive Ion Channels

Certain developmental events are thought to be controlled by mechanical tension, but the nature of the transduction mechanism for sensing and responding to tension changes is unknown. A good candidate for such a sensing system would be stretch-activated (SA) ion channels, a type of mechanosensitive (MS) ion channel found in many preparations including the oocytes or embryos of ascidians, fish, and amphibians. To test the hypothesis that SA channel activation is important for early embryogenesis, we treated amphibian and ascidian eggs and embryos with inhibitors of MS ion channels. Xenopus laevis eggs and embryos were treated with gadolinium (Gd³⁺) concentrations up to 100 times the K_d for SA channel inhibition. Boltenia villosa eggs and embryos were exposed to three agents (Gd³⁺, tubocurarine, and gallamine) which are known to block SA channels in other organisms. None of these drugs interfered with morphogenesis in a manner that would suggest SA channel activity is critical to early embryogenesis.     

A biomechanical perspective on the use of forelimb length as a measure of sexual selection in frogs

Differences in forelimb length between male and female frogs and between amplexing and non-amplexing males have been interpreted to be the results of sexual selection on forelimb length. The causal feature of the forelimb that has been posited to cause such selection is the observation that non-amplexing males attempt to disrupt breeding by prying amplexing males from females. A biomechanical model of forelimb function suggests that total length per se may not be the most appropriate measure to use. There are more functionally significant aspects of forelimb morphology, such as lever arm lengths, that should influence amplexing ability and may make measures of overall forelimb length misleading. This example highlights the relevance of functional analysis to current questions in evolutionary biology that rely on postulated roles for morphological structures under selection.     

Effects of genotype,habitat, and seasonal variation on iridoid glycoside content of Plantago lanceolata (Plantaginaceae) and the implications for insect herbivores

Summary We investigated the effects of genotype, habitat, and seasonal variation on production of the iridoid glycosides, aucubin and catalpol, in leaves of the common weed Plantago lanceolata. Two genotypes, one each from a lawn and an adjacent abandoned hayfield population, were clonally replicated in the greenhouse, and then planted back into the two habitats. One quarter of the plants from each treatment were harvested on each of four dates, at approximately two-week intervals. Over the course of the growing season, and in both habitats, we found a significant increase in the concentration of both aucubin and catalpol in P. lanceolata leaves. The genotypes differed in their response to environmental variation, both in time and between sites, as indicated by significant genotype x date and genotype x site interactions. Early in the season, habitat (lawn or field) had a greater effect on iridoid glycoside concentration than did plant genotype, but later in the season, plant genotype was more influential in determining the iridoid glycoside concentration. Thus, the relative palatability of Plantago genotypes to specialist and generalist herbivores may vary in time and space.     

Probable herpesvirus infection in an eastern cottontail (Sylvilagus floridanus).

One wild eastern cottontail (Sylvilagus floridanus) from Milwaukee County, Wisconsin was necropsied. The lungs contained numerous multifocal, circumscribed, tan foci; the spleen was markedly enlarged and had a mottled reddish tan color; and the brain had a red to tan friable tract in the left hemisphere. Microscopically, the lung had a severe bronchiolitis and pneumonia. The bronchiolitis was characterized by epithelial cells containing eosinophilic intranuclear inclusion bodies. The encephalomalacia of the left cerebral cortex featured tissue disruption and astrocytes or neurons containing intranuclear inclusion bodies. Herpesvirus particles were found within the bronchiolar epithelial cells. Based on histopathological and ultrastructural findings, a herpesvirus seemed the most likely etiologic agent.